The present invention relates to an improved process for the continuous production of polyurethane and polyurethane urea elastomers by reaction of polyisocyanates with polyhydroxy compounds and/or polyamine compounds having molecular weights of 400 to 10,000 and chain-extending agents having a molecular weight below 400 and, optionally monofunctional compounds, optionally in the presence of activators, stabilizers, lubricants and other additives known in the art. Thermoplastic polyurethane and polyurethane urea elastomers obtained by reaction of polyisocyanates with polyhydroxy compounds and/or polyamino compounds having molecular weights of 400 to 10,000 and chain-extending agents having a molecular weight below 400 and, optionally, monofunctional compounds, optionally in the presence of activators, stabilizers, lubricants and other additives known in the art, are described in detail in Kunststoff-Handbuch (Vol. VII) by Vieweg-Hochtlen, Carl-Hanser-Verlag. There are various known processes for the production of these elastomers on an industrial scale; see, e.g., German Offenlegungsschriften 1,106,959, 1,157,722, 1,165,852, 2,059,570, 3,302,564, 2,423,764, 2,302,564, 2,447,368, 2,549,372, 2,823,762, 2,842,806, and 3,223,424.
A continuous process in which the elastomers are produced in a twin-screw extruder with co-rotating shafts and self-cleaning screw geometry at temperatures of 70.degree. to 260.degree. C. is described in German Offenlegungsschriften 2,842,806 and 2,854,386. The disadvantage of this process is that the components are very thinly liquid at the temperatures mentioned, the mixing effect obtained by two co-rotating shafts is not great and the residence time is too short for a complete reaction. To achieve complete reaction, the products formed have to be after-treated in expensive apparatus and have a more or less large gel content which prevents them from being used for extrusion to very thin films. Despite thermal after-treatment, the elastomers formed remain unstable in their properties such as flow, demoldability, gel content and degree of branching, which greatly reduces the dependability of supply to customers of elastomer products for the reliable and satisfactory production of extrudates or for the production of viscosity-stable solutions for coating purposes.
German Offenlegungsschrift 2,302,564 describes small-volume, stirred mixing chambers and mixing nozzles for mixing the starting components for the production of polyurethane and polyurethane urea elastomers. Mixing nozzles are known elements for mixing liquids. Detailed particulars of the geometry of the mixing nozzle and the flow rates are not provided. In the Examples, a mixing head rather than mixing nozzles is used for the production of the polymers. A process using a mixing nozzle is not described.
German Offenlegungsschrift 2,823,762 describes a continuous process in which the starting components are passed through a static premixer, in which they are intermixed, the product temperature being so low that a reaction is largely avoided, thus preventing the products from caking. Although thorough mixing is achieved by this process, separation in the reaction zone is not prevented by suppression of the reaction at low temperatures. The partly reacted mixture does not have sufficient reaction time in the following step to react out completely and uniformly. Accordingly, the problem addressed by the present invention was to improve the existing process for the continuous production of polyurethane and polyurethane urea polymers by reaction of polyisocyanates with polyhydroxyl compounds and/or polyamine compounds having molecular weights of 400 to 10,000 and chain-extending agents having a molecular weight below 400 and, optionally, monofunctional compounds, optionally in the presence of activators, stabilizers, lubricants and other additives known in the art, in a twin-extruder with co-rotating shafts and self-cleaning screw geometry at temperatures of 70.degree. to 260.degree. C. to such an extent that
a) the components are mixed and, at the same time, are very finely dispersed, PA1 b) rotating parts should not cause any sealing problems relative to the outside environment during mixing, PA1 c) no caking of product should occur in the mixing units during mixing and PA1 d) there should be no caking or blockages in the system, PA1 e) the system is easy to clean, PA1 f) the end product has reacted out to a greater extent after leaving the twin-screw extruder, PA1 g) changes in the properties of the end product after production, such as increases in viscosity, are small, and PA1 h) better extrusion qualities are obtained.